U.S. patent application number 10/598565 was filed with the patent office on 2009-10-08 for object position estimation.
This patent application is currently assigned to KONINKLIJKE PHILIPS ELECTRONICS, N.V.. Invention is credited to Esko Olavi Dijk.
Application Number | 20090251996 10/598565 |
Document ID | / |
Family ID | 34960721 |
Filed Date | 2009-10-08 |
United States Patent
Application |
20090251996 |
Kind Code |
A1 |
Dijk; Esko Olavi |
October 8, 2009 |
OBJECT POSITION ESTIMATION
Abstract
A system for determining the position of an object (8) in a
space (10) defined by surfaces (11, 12) comprises at least a first
transducer (1), a second transducer (2) and a processing device.
The transducers are arranged at a mutual spacing (D). The
processing device is arranged for determining the times of arrival
of both acoustic signals transmitted between the object and each of
the transducers (1, 2) and their reflections. On the basis of the
difference in the times of arrival of clusters of acoustic signals
and the associated reflections the processing device can determine
which surface (11, 12) the indirect acoustic signals were reflected
by, thus providing additional position information.
Inventors: |
Dijk; Esko Olavi;
(Eindhoven, NL) |
Correspondence
Address: |
PHILIPS INTELLECTUAL PROPERTY & STANDARDS
P.O. BOX 3001
BRIARCLIFF MANOR
NY
10510
US
|
Assignee: |
KONINKLIJKE PHILIPS ELECTRONICS,
N.V.
EINDHOVEN
NL
|
Family ID: |
34960721 |
Appl. No.: |
10/598565 |
Filed: |
February 24, 2005 |
PCT Filed: |
February 24, 2005 |
PCT NO: |
PCT/IB2005/050679 |
371 Date: |
September 5, 2006 |
Current U.S.
Class: |
367/127 ; 367/99;
702/150; 702/152 |
Current CPC
Class: |
G01S 5/22 20130101 |
Class at
Publication: |
367/127 ; 367/99;
702/150; 702/152 |
International
Class: |
G01S 3/80 20060101
G01S003/80; G01S 15/00 20060101 G01S015/00; G06F 15/00 20060101
G06F015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 9, 2004 |
EP |
04100950.7 |
Claims
1. A device (20) for determining the position of an object (8) in a
space (10) defined by surfaces (11, 12), the device being arranged
for cooperating with an acoustic transducer unit so as to detect
acoustic signals transmitted between the object and the transducer
unit including their reflections, and for deducing the position of
the object from the detected acoustic signals and their
reflections, wherein the acoustic transducer unit comprises at
least a first transducer (1) and a second transducer (2) arranged
at a mutual spacing (D), and wherein the device (20) is further
arranged for determining the times of arrival of the detected
acoustic signals and their reflections, and for associating
reflections with surfaces (11, 12) on the basis of the order of the
times of arrival of the reflections and the correspondence of said
times of arrival with the respective transducers (1, 2) so as to
derive position information from said order.
2. The device according to claim 1, further arranged for detecting
any reversal in the times of arrival of the reflections.
3. The device according to claim 1, further arranged for comparing
the order in which reflections of an acoustic signal are detected
with the order in which the associated acoustic signal is
detected.
4. The device according to claim 1, further arranged for
determining the order in which the acoustic signals are
detected.
5. The device according to claim 1, further arranged for matching
the detected acoustic signals with predetermined templates.
6. The device according to claim 1, wherein the transducers (1, 2)
are arranged for detecting acoustic signals.
7. The device according to claim 1, wherein the transducers (1, 2)
are arranged for producing acoustic signals.
8. The device according to claim 1, wherein the acoustic signals
are ultrasonic signals.
9. The device according to claim 1, wherein the transducer unit
comprises at least three transducers (1, 2, 3) arranged in a
two-dimensional pattern so as to obtain three-dimensional position
information.
10. The device according to claim 1, further arranged for
determining the times of arrival (t1, t2, t3, t4, . . . ) of the
acoustic signals and their reflections relative to the time of
transmission of those signals.
11. A system for determining the position of an object in a space
defined by surfaces (11, 12), the system comprising a first
transducer (1), a second transducer (2) and a device (20) according
to claim 1.
12. A method of determining the position of an object (8) in a
space (10) defined by surfaces (11, 12) using an acoustic
transducer unit, the method comprising the steps of detecting
acoustic signals transmitted between the object and the transducer
unit including their reflections, and deducing the position of the
object from the detected acoustic signals and their reflections,
wherein the acoustic transducer unit comprises at least a first
transducer (1) and a second transducer (2) arranged at a mutual
spacing (D), and wherein the times of arrival of the detected
acoustic signals and their reflections are determined, and
reflections are associated with surfaces (11, 12) on the basis of
the order of the times of arrival of the reflections and the
correspondence of said times of arrival with the respective
transducers (1, 2) so as to derive position information from said
order.
13. The method according to claim 12, further comprising the step
of detecting any reversal in the times of arrival of the
reflections.
14. The method according to claim 12, further comprising the step
of comparing the order in which reflections of an acoustic signal
are detected with the order in which the associated acoustic signal
is detected.
15. The method according to claim 12, further comprising the step
of determining the order in which the acoustic signals are
detected.
16. The method according to claim 12, further comprising the step
of matching the detected acoustic signals with predetermined
templates.
17. The method according to claim 12, wherein the transducers (1,
2) are arranged for detecting acoustic signals.
18. The method according to claim 12, wherein the transducers (1,
2) are arranged for producing acoustic signals.
19. The method according to claim 12, wherein the acoustic signals
are ultrasonic signals.
20. The method according to claim 12, wherein the transducer unit
comprises at least three transducers (1, 2, 3) arranged in a
two-dimensional pattern so as to obtain three-dimensional position
information.
21. The method according to claim 12, further comprising the step
of determining the times of arrival (t1, t2, t3, t4, . . . ) of the
acoustic signals and their reflections relative to the time of
transmission of those signals.
22. A computer program product for carrying out the method
according to claim 12.
Description
[0001] The present invention relates to object position estimation.
More in particular, the present invention relates to a device and a
system for determining the position of an object in a space defined
by surfaces.
[0002] It is well known to determine the submersion depth of a
submarine in sea water using the transmission time of sound
signals. Using acoustic signals to determine the position of an
object in air is far less common.
[0003] European Patent Application 03101098.1 describes a position
estimation system for estimating a position of an object in a room
using ultrasound. This system detects not only the shortest route
signal but also reflection signals so as to obtain more information
on the position of the object. The detected signals are compared
with templates and a matching template defines the position in the
room.
[0004] Although the system of European Patent Application
03101098.1 is very effective, is has the drawback that it cannot
distinguish between reflections off different surfaces (that is,
walls, ceiling and floor). In other words, when detecting a
reflection signal the system cannot determine whether the
reflection signal was reflected by a wall on the left-hand side of
the room or on the right-hand side. As a result, some ambiguity
with regard to the position of the object may remain.
[0005] It is an object of the present invention to overcome these
and other problems of the Prior Art and to provide a device for
determining the position of an object that allows the position of
the object to be determined with greater accuracy.
[0006] It is another object of the present invention to provide a
device for determining the position of an object that can
distinguish between signals reflected by different surfaces.
[0007] It is further object of the present invention to provide a
system for and a method of determining the position of an
object.
[0008] Accordingly, the present invention provides a device for
determining the position of an object in a space defined by
surfaces, the device being arranged for cooperating with an
acoustic transducer unit so as to detect acoustic signals
transmitted between the object and the transducer unit including
their reflections, and for deducing the position of the object from
the detected acoustic signals and their reflections, [0009] wherein
the acoustic transducer unit comprises at least a first transducer
and a second transducer arranged at a mutual spacing, and [0010]
wherein the device is further arranged for determining the times of
arrival of the detected acoustic signals and their reflections, and
for associating reflections with surfaces on the basis of the order
of the times of arrival of the reflections and the correspondence
of said times of arrival with the respective transducers so as to
derive position information from said order.
[0011] By using at least two transducers which are spaced apart,
and determining the times of arrival of the reflections of the
acoustic signals, it is possible to distinguish between reflections
caused by different surfaces as the times of arrival of the
reflections will be determined by these surfaces. As a result, the
reflections can be associated with the reflecting surfaces, that
is, the surfaces can be identified that caused certain reflections.
The location of these surfaces relative to the transducers provides
valuable position information allowing a reliable determination of
the position of the object. Additionally determining the times of
arrival of the detected direct, that is non-reflected acoustic
signals provides additional position information allowing the
position of the object to be deduced with greater accuracy.
[0012] More in particular, the indirect, that is reflected signals
associated with the first and the second transducers may arrive in
reverse temporal order, depending on the reflecting surface. In
this way, the relative times of arrival of the reflected signals
corresponding with the first and the second transducer provide an
indication of the surface causing the reflection and of the
trajectory of the reflections and hence of the position of the
object.
[0013] In a preferred embodiment, the device of the present
invention is further arranged for detecting any reversal in the
times of arrival of the reflections. That is, a reversal of the
times of arrival of the reflections of the acoustic signal received
at the transducers of the transducer unit, and/or a reversal of the
times of arrival of the reflections of the acoustic signal produced
by the transducers of the transducer unit, is used to identify the
surface causing the reflection.
[0014] In an advantageous embodiment, the device is further
arranged for comparing the order in which reflections of an
acoustic signal are detected with the order in which the associated
acoustic signal is detected. Thus, by including the direct acoustic
signal, an improved comparison of the detection times is achieved
and the reflection surfaces can be identified with greater
accuracy, leading to a better position estimation.
[0015] In a preferred embodiment, the device of the present
invention is further arranged for determining the order in which
the acoustic signals are detected. That is, the order of the direct
signal detection times associated with the at least two transducers
is used to derive position information. It will be understood that
this order is not used to identify a surface but to deduce position
information directly, in particular information concerning the
position of the object relative to the transducer unit, for example
information indicating whether the object is positioned to the left
or to the right of the transducer unit.
[0016] It is possible to determine the position of an object solely
on the basis of the times of arrival of the acoustic signals and
the associated reflections, as these times of arrival define the
transmission paths of the acoustic signals including the
reflections. However, in an advantageous embodiment the device of
the present invention is further arranged for matching the detected
acoustic signals with predetermined templates. In this embodiment,
templates of the acoustic signals typically received in the space
concerned are made and stored, and the acoustic signals and
reflections detected when determining a position are matched with
the templates, the best match providing an estimate of the
position. This technique of template matching is described in more
detail in the above-mentioned European Patent Application
03101098.1. The present invention provides a valuable addition to
said template matching technique and removes any remaining
ambiguities.
[0017] In a first embodiment, the transducers are arranged for
detecting acoustic signals. In this embodiment, the acoustic
signals could be produced by the object or by an external source.
The device of the present invention is in this embodiment coupled
to the transducers.
[0018] In a second embodiment, the transducers are arranged for
producing acoustic signals. In this embodiment, the acoustic
signals are produced by the transducers and could be detected by a
further transducer (detector) located in the object of which the
position is to be determined. The device of the present invention
is in this embodiment suitably coupled to the object. That is, the
device may be located in the object or may be coupled to the object
to receive detection signals from the further transducer.
[0019] In a third embodiment, the transducers are arranged for both
producing and detecting acoustic signals. In this embodiment, the
acoustic signals could be produced by the transducers, be reflected
or re-transmitted by the object and then be detected by the same
transducers. The device of the present invention is in this
embodiment coupled to the transducers and may comprise a circuit
for producing suitable transducer excitation signals.
[0020] In the third embodiment, the acoustic signals produced by
the two (or more) transducers can be distinguished, for example by
having slightly different frequencies or containing identification
signals when transmitted simultaneously, or by transmitting the
acoustic signals consecutively, preferably at a predetermined time
interval.
[0021] It is preferred that the acoustic signals are ultrasonic
signals. By using signals which are not audible, any interference
with music or any discomfort for the user is avoided. However, it
is also possible to use sound signals, that is, audible
signals.
[0022] In a preferred embodiment, only two transducers are used.
This, however, allows the position of an object to be determined in
a single plane only. In an advantageous alternative embodiment,
therefore, there are at least three transducers arranged in a
two-dimensional pattern so as to obtain three-dimensional position
information. The pattern could for instance be a triangle or a
square. Such an arrangement allows the position of an object to be
determined in two orthogonal planes, that is, in three dimensions,
for example by applying the present invention in each plane
separately, or by directly determining the three-dimensional
position of the object.
[0023] Advantageously, the device of the present invention is
further arranged for determining the times of arrival of the
acoustic signals and their reflections relative to the time of
transmission of those signals. This provides additional information
on the position of the object as the times of arrival of the direct
acoustic signals relative to the respective times of transmission,
and therefore the transmission times of the direct signals, are
proportional of the length of the transmission paths. Dividing this
transmission time by the speed of sound (in air approximately 343
m/s) gives the length of the transmission path.
[0024] The present invention further provides a system for
determining the position of an object in a space defined by
surfaces, the system comprising a first transducer, a second
transducer and a device as defined above. The system may comprise a
further transducer arranged in the object for detecting acoustic
signals transmitted by the first and second transducers. It will be
understood that the system may include a transducer unit which
comprises more than two transducers, for example three or four.
[0025] The present invention also provides a method of determining
the position of an object in a space defined by surfaces using an
acoustic transducer unit, the method comprising the steps of
detecting acoustic signals transmitted between the object and the
transducer unit including their reflections, and deducing the
position of the object from the detected acoustic signals and their
reflections, [0026] wherein the acoustic transducer unit comprises
at least a first transducer and a second transducer arranged at a
mutual spacing, and [0027] wherein the times of arrival of the
detected acoustic signals and their reflections are determined, and
reflections are associated with surfaces on the basis of the order
of the times of arrival of the reflections and the correspondence
of said times of arrival with the respective transducers so as to
derive position information from said order.
[0028] In addition, the present invention provides a computer
program product for carrying out the method as defined above.
[0029] The present invention will further be explained below with
reference to exemplary embodiments illustrated in the accompanying
drawings, in which:
[0030] FIG. 1 schematically shows, in plan view, a room in which
the position of an object is located in accordance with the Prior
Art.
[0031] FIG. 2 schematically shows acoustic pulses and their arrival
times as used in the Prior Art.
[0032] FIG. 3 schematically shows, in plan view, a room in which
the position of an object is located in accordance with the present
invention.
[0033] FIG. 4 schematically shows acoustic pulses and their arrival
times as used in the present invention.
[0034] FIG. 5 schematically shows a device for determining the
position of an object in accordance with the present invention.
[0035] FIG. 6 schematically shows alternative transducer
arrangements in accordance with the present invention.
[0036] The room 10 shown merely by way of non-limiting example in
FIG. 1 is defined by side walls 11 and 12, a front wall 13 and a
back wall 14. The room may also have a ceiling and a floor which
are not shown in FIG. 1 for the sake of clarity of the
illustration.
[0037] In accordance with the Prior Art, a single transducer 1 is
arranged in the room, in the example shown at the front wall 13. An
object 8, the position of which is to be determined, is located in
the room 10.
[0038] Acoustic signals (that is, sound or ultrasound signals)
emitted by the object 8 will propagate in multiple directions. One
such propagation path, also known as transmission path, forms the
shortest route from the object 8 to the transducer 1. An acoustic
signal following this "line-of-sight" path d.sub.1 will be detected
first by the transducer 1, as the alternative paths involving
reflections, such as the paths d.sub.1' and d.sub.1'', are longer.
That is, the signal of any paths involving reflections off the side
walls 11 and 12 will be slightly delayed with respect to the direct
path d.sub.1. This delay, which will later be explained in more
detail with reference to FIG. 2, provides information regarding the
position of the object 8.
[0039] In FIG. 1, "virtual transducers" 1', 1'' and 1''' are shown.
Virtual transducers 1', 1'' are mirror images of the actual
transducer 1, mirrored relative to the walls 11 and 12. Virtual
transducer 1''' is itself a mirror image of the virtual transducer
1' relative to the wall 12. These virtual transducers merely serve
to clarify the geometry of the transmission paths, as it will be
understood that transducer 1 is the actual transducer and that all
actual transmission paths are located inside the room 10. Thus the
first reflection against the left wall 11 follows the transmission
path d.sub.1', the second reflection against the right wall 12
follows the transmission path d.sub.1'' while the third reflection,
reflecting first against the right wall 12 and then against the
left wall 11, follows the transmission path d.sub.1'''.
[0040] In FIG. 2 the amplitude (A) of detected acoustic pulses is
schematically illustrated. These pulses, which are detected by the
transducer 1 of FIG. 1, are detected at various points in time
(t).
[0041] As can be seen in FIG. 2, each transmission path causes an
acoustic signal to be detected by the transducer 1: at t.sub.1, the
transducer 1 detects the direct ("line-of-sight") path d.sub.1, at
t.sub.2 the first reflection via transmission path d.sub.1', at
t.sub.3 the second reflection via transmission path d.sub.1'' and
at t.sub.4 the third reflection via transmission path d.sub.1'''.
These times of arrival provide valuable information on the position
of the object 8. However, it is not possible to determine whether a
reflection was caused by the left wall 11 or the right wall 12. As
a result, the position of the object 8 as detected is ambiguous and
no distinction can be made between the actual object 8 and a
"phantom" object 9 which is located at the same distance as the
object 8 but at a position mirrored relative to the center line of
the room 10. The present invention aims to solve this problem.
[0042] In accordance with the present invention, both a first
transducer 1 and a second transducer 2 are arranged at the front
wall 13, as is schematically shown in FIG. 3. As before an object
8, the position of which is to be determined, is located in the
room 10. It will be understood that the room 10 merely serves as an
example and that the present invention can also be utilized in any
other space having at least two surfaces, such as walls, a ceiling
and/or a floor. The invention can therefore also be used in, for
example, a space between two buildings.
[0043] In the following discussion it will be assumed that the
transducers 1 and 2 receive acoustic signals emitted by the object
8. The invention is, however, not so limited and embodiments can be
envisaged in which the transducers emit acoustic signals which are
received, or reflected, by the object 8. Alternatively, the
transducers 1 and 2 may receive acoustic signals that are emitted
by another transducer (not shown) and reflected by the object
8.
[0044] Acoustic signals (that is, sound or ultrasound signals)
emitted by the object 8 will again propagate in multiple
directions. Two such propagation paths, also known as transmission
paths, form the shortest routes from the object 8 to the
transducers 1 and 2 respectively. An acoustic signal following
these "line-of-sight" paths d.sub.1 and d.sub.2 will be detected
first by the transducers 1 and 2 respectively, as the alternative
paths involving reflections, such as the paths d.sub.1' and
d.sub.2', are longer. That is, the signal of any paths involving
reflections off the side walls 11 and 12 will be slightly delayed
with respect to the direct paths d.sub.1 and d.sub.2. This delay,
which will later be explained in more detail with reference to FIG.
4, provides information on the position of the object 8.
[0045] In the example of FIG. 3, the object 8 is located to the
left of the middle of room 10, while the transducers 1 and 2 are
located approximately at the center of front wall 13. As a result,
the direct path d.sub.1 is slightly shorter than the direct path
d.sub.2 and the acoustic signal from the object 8 will reach
transducer 1 before it reaches transducer 2. This is schematically
illustrated in FIG. 4, where the detected signal amplitude (A) is
shown at various points in time (t). At t.sub.1, transducer 1 is
the first to detect a signal (path d.sub.1), followed by transducer
2 at t.sub.2 after a short delay. This time delay
.DELTA.=(t.sub.2-t.sub.1) already indicates, in the geometry of
FIG. 3, that the object 8 is located to the left of the middle of
room 10. It can be seen from FIG. 3 that the time delay .DELTA.
would be equal to zero if the object 8 were located in the middle
of the room, opposite the transducers 1 and 2. Similarly, the time
delay .DELTA. would be negative (transducer 1 receiving the
acoustic signal later than transducer 2) is the object 8 were
located to the right of the middle of the room.
[0046] It is noted that this time delay .DELTA. is due to the
position of the object 8 and the spacing D of the transducers 1 and
2. In the Prior Art arrangements where only a single microphone or
other transducer is used, this time delay .DELTA. cannot be
detected and consequently valuable location information is
lost.
[0047] At t.sub.3, the first transducer 1 receives a signal which
has been reflected by the left side wall 11. This signal has
followed the path d.sub.1' indicated in FIG. 3. At t.sub.4, the
second transducer 2 receives the counterpart signal which has
followed the path d.sub.2' of FIG. 3. As shown schematically in
FIG. 3, the reflections off the left wall 11 can be modeled as
paths leading towards virtual transducers 1' and 2', the positions
of which are mirror images relative to the wall 11 of the actual
positions of the transducers.
[0048] Similarly, reflections off the right wall 12 can be modeled
as paths d.sub.2'' and d.sub.1'' leading to virtual transducers 2''
and 1'' respectively, the positions of the virtual transducers
being mirror images relative to the wall 12. It is noted that the
path d.sub.2'' is closer to the (actual) transducers 1 and 2 than
the path d.sub.1'' is. As a result the path d.sub.2'' is shorter
and the signal will reach the second transducer 2 first. This is
shown in FIG. 4 where the second transducer 2 receives a signal at
t.sub.5, while the first transducer 1 receives the same signal at
t.sub.6. This reversal of the order of receipt is another valuable
indication of the position of object 8. In particular, this
reversal indicates that the signal received at t.sub.5 and t.sub.6
is reflected by the right wall 12 instead of the left wall 11. It
is again noted that this reversal cannot be detected by
arrangements having only a single transducer, or by arrangements
where no spacing D is present.
[0049] As can be seen, further reflections off the right wall are
possible, resulting in paths d.sub.1''' and d.sub.2''' towards
virtual transducers 1''' and 2''' respectively (the paths
d.sub.1''' and d.sub.2''' inside the room 10 are not shown for the
sake of clarity of the illustration but are of course analogous to
the reflections shown in FIG. 1). The positions of the virtual
transducers 1''' and 2''' are the mirror image relative to the wall
12 of the positions of virtual transducers 1' and 2' respectively.
These further reflections are received at t.sub.7 and t.sub.8 (FIG.
4) respectively. Although further signals (not shown) resulting
from further reflections may also be used, it is preferred to use
the first three or four pairs of signals (for example the first
eight points in time t.sub.1-t.sub.8) only. The time interval T in
which the acoustic signals are detected therefore extends so as to
include at least the first and the second reflection pairs, and
preferably also the third reflection pair. It is noted that the
time interval T may start at a common reference point in time
t.sub.0 (denoted 0 in FIG. 4) to produce "absolute" times of
arrival, the point in time to preferably being the moment of
transmission of the acoustic pulses. Those skilled in the art will
be able to utilize known mechanisms providing time synchronization
of the transducers 1 and 2 when used as signal detectors on the one
hand and any transmitting transducer in the object on the other
hand, so as to establish the common reference point in time. For
example, the transmitted signals could be provided with a time
stamp consisting of, for example, a code word (digital) or a code
signal (analog). Alternatively, received signals could be
re-transmitted so as to provide a transmission time indication.
[0050] In FIG. 4 it is indicated by which transducer each signal is
received. The "normal" order being 1-2, it can be seen that the
second reflections, received at t.sub.5 and t.sub.6, are received
in reverse order due to the transmission paths involving the right
wall 12. Using the order in which the signals are received, it can
therefore be determined that the signal pair received at t.sub.1
and t.sub.2 are direct path signals, that the signals received at
t.sub.3 and t.sub.4 are indirect signals reflected by the left wall
11 and that the signals received at t.sub.5 and t.sub.6 are
indirect signals reflected by the right wall 12.
[0051] When the geometry of the room 10 is known, it is possible to
determine the location of the object 8 on the basis of the times of
arrival t.sub.1 to t.sub.8. In particular, the relative time
differences t.sub.3-t.sub.1 and t.sub.6-t.sub.1 provide information
on the lengths of the paths d.sub.1, d.sub.1' and d.sub.1''.
Identifying the reflecting surfaces on the basis of the order in
which the reflections are detected indicates the general direction
of these paths. Using well-known geometric formulae, the position
of the object 8 may then be unambiguously determined.
[0052] Although it is possible to determine the position of the
object 8 solely on the basis of the times of arrival of the
detected acoustic pulses and their reflections, it is preferred to
additionally use template matching of the detected signals and
reflections. This involves making templates of the received
acoustic signals and their reflections for a large number of
possible positions in the room 10 and storing these templates. When
determining the position of an object in the room, the signal
amplitudes (envelope) of the received signals are compared with the
stored templates. The stored position corresponding with the best
match is the desired position. This technique is described in more
detail in the above-mentioned European Patent Application
03101098.1, the entire contents of which are hereby incorporated in
this document.
[0053] It is noted that the comparison carried out in the
above-mentioned template matching method may involve a simple
subtraction or a least-squares comparison but preferably a
correlation of each acoustic signal with a plurality of templates.
The mathematical technique of correlation is well known and needs
no further explanation. The template having the highest, that is
"best" correlation with a certain detected acoustic signal is
selected. As the object position corresponding with the particular
template is previously stored, this position is then retrieved to
yield the determined object position.
[0054] It has been found that the present invention, when used in
addition to template matching, provides a significant improvement
of the method of European Patent Application 03101098.1. In
particular, the said method may produce ambiguous results in the
presence of noise and/or when a large number of reflections is
detected. The present invention removes these ambiguities by
providing additional position information which may be suitably
combined with the position information provided by the template
matching method to yield an accurate position determination. In a
particularly advantageous embodiment, therefore, a template
matching is carried out, providing a "shortlist" of not one but a
(small) number of best matches (that is, matching templates), for
example three, five, or ten. A position determination according to
the present invention is also carried out, yielding an additional
determined position. This additional position (based on the
reflection detection order) is then compared with the
above-mentioned "shortlist" to select the best template-based
position corresponding with the additional reflection-based
position. It will be clear that this combined method provides an
excellent possibility for error checking: when there is no
template-based position that corresponds with a reflection-based
position, an error must have been made. Such errors may be due to
noise, moving other objects in the space concerned, and other
causes.
[0055] The example of FIGS. 3 and 4 involves position detection in
a plane, that is, in two dimensions. It will be understood that the
present invention can also be utilized for three-dimensional
position detection, as will later be explained with reference to
FIGS. 6a-d.
[0056] A device for determining the position of an object in a room
is schematically shown in FIG. 5. The exemplary device 20 comprises
an interface unit 21, a processor unit 22, a memory unit 23 and an
input/output (I/O) unit 24. A first transducer 1 and a second
transducer 2 are coupled to the device 20 via the interface unit 21
which provides suitable signal conversions. The processor unit 22
preferably comprises a microprocessor capable of executing computer
programs stored in memory unit 23. In addition to computer programs
for e.g. template matching and/or signal processing, the memory
unit 23 may also store templates. A computer program may be loaded
into the memory unit 23 from a suitable carrier device such as a CD
or DVD.
[0057] The transducers may be used for detecting acoustic signals,
producing acoustic signals, or both. In one embodiment, the
transducers 1 and 2 produce acoustic signals containing an
identification, such as a (digital) code word, or a particular
unique frequency. The object 8 may, in that particular embodiment,
contain a single transducer and may further contain the device 20
or, alternatively, transmission means for transmitting the signals
produced by the transducers to a remote device 20. Embodiments can
be envisaged in which the transducer unit containing the
transducers 1 and 2 as well as the device 20 are accommodated in
the object 8, and in which a single transducer is mounted on a wall
of the room 10.
[0058] Suitable transducer arrangements in accordance with the
present invention are schematically shown in FIGS. 6a-d. In the
example of FIG. 6a, the transducers 1 and 2 are positioned at a
horizontal spacing D.sub.x, while in FIG. 6b the transducers 1 and
2 are arranged vertically at a spacing D.sub.y. Either arrangement
allows the position of an object to be determined in a single
(horizontal or vertical) plane only. The two-dimensional
arrangement of FIG. 6c allows a position to be determined in both
the horizontal and the vertical plane using three transducers 1, 2
and 3. The horizontal spacing D.sub.x and the vertical spacing
D.sub.y may also be achieved by an arrangement of four transducers
1-4 as shown in FIG. 6d. It will be understood that other
arrangement are also possible. For instance, more than two
transducers could be used in any plane, such as an arrangement of
three or four transducers in line. Such an arrangement provides
more timing information at the cost of additional transducers. It
will be understood that the present invention can be practiced
using only two transducers in any plane.
[0059] Although the transducers 1 and 2 in FIG. 3 are arranged in
the plane of the front wall 13, this is not essential and the plane
in which the transducers lie could be situated at an acute or even
right angle relative to the front wall 13. It will be understood
that the transducers 1 and 2 can also be placed on other walls or
surfaces.
[0060] The present invention is based upon the insight that using
two transducers which are spaced apart allows reflections off
surfaces to be identified on the basis of their relative time
delays. The present invention benefits from the further insight
that the reflections of acoustics signals can be used to determine
the position of an object in a room.
[0061] Under computer program product should be understood any
physical realization, e.g. an article of manufacture, of a
collection of commands enabling a processor--generic or special
purpose--, after a series of loading steps to get the commands into
the processor, to execute any of the characteristic functions of an
invention. In particular the computer program product may be
realized as program code, processor adapted code derived from this
program code, or any intermediate translation of this program code,
on a carrier such as e.g. a disk or other plug-in component,
present in a memory, temporarily present on a network
connection--wired or wireless--, or program code on paper. Apart
from program code, invention characteristic data required for the
program may also be embodied as a computer program product.
[0062] It is noted that any terms used in this document should not
be construed so as to limit the scope of the present invention. In
particular, the words "comprise(s)" and "comprising" are not meant
to exclude any elements not specifically stated. Single (circuit)
elements may be substituted with multiple (circuit) elements or
with their equivalents.
[0063] It will be understood by those skilled in the art that the
present invention is not limited to the embodiments illustrated
above and that many modifications and additions may be made without
departing from the scope of the invention as defined in the
appending claims.
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